1. Field of the Invention
This invention relates to a solid-state imaging or image pickup apparatus adapted to pick up an image of an object by a solid-state image sensor in which photoelectric conversion elements are arranged in a matrix form, which is applied to a television camera apparatus of the standard television system, e.g., the NTSC (National Television System Committee) system, PAL system etc, where an interlaced scanning is carried out.
Such standard television systems such as the NTSC system, etc., use interlaced scanning in which scanning lines of odd fields and scanning lines of even fields are alternately positioned.
2. Description of the Prior Art
In a solid-state imaging apparatus using a solid-state image sensor such as a CCD (Charge Coupled Device) in which photoelectric conversion elements are arranged in a matrix form, approaches have been employed to allow the sensor to be operative in an operational mode called a field readout mode or an operational mode called a frame readout mode, both of which produce an image pickup output of the interlaced scanning type.
For example, in an interline transfer type CCD image sensor, in operation in the field readout mode, as shown in FIG. 6 of the accompanying drawings, image pickup charges A.sub.i from photoelectric conversion elements of odd columns and image pickup charges B.sub.i from photoelectric conversion elements of even columns (which are respectively adjacent to each other) are transferred to vertical transfer registers by using readout pulses every vertical blanking period. Charges from vertically adjacent pairs of photoelectric conversion elements (odd and even) are added together, with the pairing being alternated each field (so that a given charge is added to the charge from above in one field and to the charge below the next field) to line-sequentially read out image pickup charges (A.sub.i +B.sub.i) then (B.sub.i +A.sub.i+1) in successive fields. The charges are transferred through a horizontal transfer register from the vertical transfer registers during an image period to thereby obtain an image pickup output corresponding to the interlaced scanning.
In the case of the operation in the frame readout mode, an approach is employed as shown in FIG. 7 to transfer, by using readout pulses every vertical blanking period, image pickup charges A.sub.i from photoelectric conversion elements of odd columns and image pickup charges B.sub.i from photoelectric conversion elements of even columns to the vertical transfer registers in alternate intervals. Then one after another every field those image pickup charges A.sub.i, B.sub.i of respective fields are line-sequentially read out through the horizontal transfer register from the vertical transfer registers during an image period to thereby obtain an image pickup output corresponding to the interlaced scanning.
In addition, it has also been proposed to provide an electronic shutter function for such image sensors in which, in the above-mentioned field readout mode, control pulses are applied to sweep away image pickup charges obtained by respective photoelectric conversion elements into the overflow drain, thereby permitting effective charge storage periods, and thus the effective shutter speed, to be variable.
However, the above techniques have certain disadvantages. In the field readout mode, the addition and mixing of image pickup charges A.sub.i of odd columns and image pickup charges B.sub.i of even columns lowers the vertical resolution (Modulation Transfer Function or MTF).
In the frame readout mode, though, as the image pickup charges A.sub.i of odd columns and image pickup charges B.sub.i of even columns adjacent thereto are separately read out, the vertical resolution (MTF) is improved compared to the field readout mode, but there are problems that with moving pictures there results an increased after-image and that the dynamic range becomes approximately one half because of the increased charge pickup time. In addition, in the case of the frame readout mode, the flicker caused by the interlaced scanning tends to become conspicuous.